Stainless Steel Grade 316: Premium Corrosion Resistance for Harsh Environments

Grade 316 at a Glance

Grade 316 is a molybdenum-bearing austenitic stainless steel designated UNS S31600, with European equivalent EN 1.4401 (X5CrNiMo17-12-2) and Japanese equivalent JIS SUS316. The intentional addition of 2.00 to 3.00 percent molybdenum raises resistance to pitting and crevice corrosion in chloride-bearing media well above that of 304, and also improves behaviour in many dilute acids. The grade is essentially non-magnetic after annealing, is readily welded and formed, and retains good toughness down to cryogenic temperatures. Product forms are covered by ASTM A240 for plate and sheet, A276 for bar, A312 for pipe, A213 for boiler and heat-exchanger tubes, and A269 for small-diameter tubing.

Chemical Composition per ASTM A240

The following limits apply to plate, sheet and strip of UNS S31600 in the annealed condition. Chromium and nickel stabilise the austenitic structure, molybdenum provides the corrosion lift, and nitrogen adds strength and pitting resistance.

Element	Percent by Weight
Carbon, max	0.08
Manganese, max	2.00
Phosphorus, max	0.045
Sulfur, max	0.030
Silicon, max	0.75
Chromium	16.00-18.00
Nickel	10.00-14.00
Molybdenum	2.00-3.00
Nitrogen, max	0.10

Mechanical Properties and Heat Treatment

Minimum mechanical requirements for annealed plate per ASTM A240 are listed below. The grade cannot be hardened by heat treatment; strength increases only through cold working. Solution annealing is normally carried out at 1010 to 1120 degrees C followed by rapid cooling, which restores corrosion resistance after hot forming or after welding heavy sections.

Property	Minimum Value
Tensile strength	515 MPa
Yield strength, 0.2 percent offset	205 MPa
Elongation in 50 mm	40 percent
Hardness, max	95 HRB / 217 HBW

Corrosion Resistance in Harsh Environments

Using minimum composition values, the pitting resistance equivalent number of 316, calculated as Cr + 3.3Mo + 16N, is about 24, compared with roughly 19 for 304; the gap widens at higher molybdenum and nitrogen contents. In practice this translates into markedly better performance in seawater splash zones, coastal atmospheres, paper-mill liquors and food-processing acids such as citric, acetic and lactic acid. Grade 316 also resists dilute sulfuric acid and phosphoric acid at ambient temperature. It is not suitable for hot concentrated hydrochloric acid, hot caustic solutions, or long-term immersion in stagnant seawater where crevice corrosion develops; chloride stress-corrosion cracking is a risk above about 60 degrees C, so service temperature and stress levels must be reviewed together.

Applications

Chemical and petrochemical process equipment and piping

Food, beverage and dairy processing plant

Pharmaceutical and biotechnology vessels

Heat exchangers and condensers in coastal power plants

Marine deck hardware, railings and coastal architecture

Textile dyeing and bleaching equipment

Frequently Asked Questions

Q1. What makes 316 more corrosion resistant than 304?
The 2.00 to 3.00 percent molybdenum addition strengthens the passive film and suppresses pitting and crevice attack in chloride media; 304 contains no molybdenum.

Q2. Is 316 suitable for seawater service?
It performs well in ambient-temperature splash and atmospheric exposure, but stagnant seawater in crevices can cause localised attack. For permanent immersion or warm seawater, duplex or super-austenitic grades are preferred.

Q3. What is the difference between 316 and 316L?
316L limits carbon to 0.030 percent maximum, which prevents chromium-carbide precipitation during welding and avoids the need for post-weld solution annealing in most sections.

Q4. Can 316 be welded?
Yes, by TIG, MIG, plasma and resistance processes. For heavy sections or service above about 425 degrees C, 316L filler metal is normally specified.

Q5. What does PREN mean?
Pitting resistance equivalent number, commonly Cr + 3.3Mo + 16N, is a comparative index of resistance to chloride pitting; higher values indicate better resistance.

Q6. Is 316 magnetic?
In the annealed condition it is essentially non-magnetic. Cold working such as bending or machining can induce slight magnetism.